Typically, a bicycle wheel comprises a rim, on which a tire, a hub and a plurality of spokes extending between the rim and the hub are mounted.
Amongst the various types of bicycle wheels, the use of the type known as “tubeless,” i.e. without an air chamber, is now widespread. In particular, in tubeless wheels, the tire is mounted airtight on the rim, so as to form an airtight annular area in which pressurized air is introduced through an inflation valve associated with the rim at a suitable hole formed in the rim.
The airtight annular area of the tubeless wheels is defined by an inner surface of the tire and by an outer surface of the rim. In particular, the rim includes a body with a substantially annular extension having a radially outer portion provided with an annular bottom wall, or upper bridge of the rim, and a pair of annular side walls, or fins, extending radially outwards from the upper bridge. The fins hold the radially inner end edges, or beads, of the tire, in a final assembled configuration of the tire, against the thrust of the pressurized air, achieving the airtight coupling between tire and rim.
The outer surface of the rim that delimits the airtight annular area is therefore defined by the radially outer surface of the upper bridge and by the axially inner surfaces of the fins.
The hole for the inflation valve is typically formed in an annular recess formed in a central annular portion of the upper bridge of the rim. The upper bridge preferably has no further holes. In particular, no holes are provided for the assembly of the spokes of the wheel; such holes are instead generally provided in a radially inner portion of the rim. In those cases in which the holes for the assembly of the spokes are present in the upper bridge, they are suitably sealed through a sealing band such as the rubber band described in US2004/0095014.
The annular recess formed in the upper bridge of the rim defines an annular channel for housing at least one of the beads of the tire, preferably for both of the beads, in an initial assembly step of the tire on the rim. In this step, the beads are housed in the annular recess so as to be pushed into contact with the side walls of the recesses. After this step, the tire is inflated by feeding pressurized air into the chamber defined between the tire and the upper bridge. In this step, the beads of the tire slide on the upper bridge, through the effect of the pressurized air, until the fins of the rim are reached, with which they couple to hold the tire against the thrust of the pressurized air in the final assembled configuration of the tire.
In the inflation step, it is necessary to ensure the airtight connection between tire and upper bridge during sliding of the beads of the tire on the upper bridge. This step is therefore very delicate and requires feeding of air at high pressure.